1. Field of the Invention
The invention relates generally to the recovery of subterranean deposits and more specifically to methods and systems for removing produced fluids from a well.
2. Description of Related Art
Horizontal coalbed methane wells are particularly susceptible to production problems caused by the presence and accumulation of solid particles in the wellbore. For example, during the life of a horizontal coalbed methane well, many tons of small coal particles, termed coal “fines”, can be co-produced along with the methane and water. In the early stages of the well, these solid particles typically pose little problem for the production process. High flow rates of both water and gas create enough velocity within the wellbore to keep the solids entrained in the production fluids and moving towards the pumping equipment installed in the well. At the pump inlet, again, the solids stay entrained in the liquid phase and are pumped from the well.
In the later stages of the life of a coalbed methane well, coal fines may begin to pose a problem. Gas flow alone may not be able to carry solids along the wellbore, resulting in those solids being left to settle in the low angle undulations of the wellbore. The solids may ultimately form a restriction to the flow of gas, and a resulting drop in production may occur. Alternatively, the settling of these solids near the pump inlet may block the inlet to the pump, thereby reducing the ability of the pump to remove water from the wellbore.
Borehole stability issues may also contribute to production problems of a well. In some cases, the wellbore can collapse and deposit large, medium and small pieces of coal in the wellbore. The cubical-shaped pieces of coal can easily form a bridge within the wellbore and restrict the flow of wellbore fluids. This restriction may cause further settling of entrained solids.
Referring to FIG. 1, a well 100 includes a wellbore 105 having a substantially vertical portion 110 and a substantially horizontal portion 115. The wellbore 105 extends from a surface 120 to a formation 123 located beneath the surface 120. A pump 125 is positioned downhole within the substantially horizontal portion 115 and is electrically connected by a transmission cable 126 to a power supply 128 positioned at the surface 120. The pump 125 is provided to remove liquids 127 (e.g. water) that are produced by the formation 123. The liquids are pumped through a tubing string 130 to a reservoir 133 at the surface 120. To illustrate an example mentioned previously, well 100 may be a coalbed methane well that is drilled into a coal formation. Deposits 135 of solid particles (e.g. coal) may accumulate within the wellbore, which could block the inlet to pump 125.
One method that has been used to overcome the problem of solids settling in the well includes injecting additional fluids, either water or gas, at some point in the well, thereby increasing fluid flow velocity. The increase in flowing velocity, however, carries a penalty in the form of additional pressure against the producing formation. Further, the production facilities must handle the additional volumes of injected fluids. Another system for clearing a wellbore uses a longitudinal movement of an agitating device in a borehole. This system may be effective at agitation, however, a sudden build-up of solids may cause the device to become lodged and render the entire mechanism unusable. Both of these systems have inefficiencies and problems that are solved by the systems and methods of the embodiments described herein.
The removal water accumulated solids from a well presents other problems related to the use of downhole pumps. Installation and removal of the pumps is complicated by having to deal with the pump cable that powers the pump motor. During pump installation, the power cable is first spliced onto the leads of the motor. The cable is then attached to the discharge tubing as the pump is lowered into the well. Various methods are used to attach the cable to the tubing, including clamps, adhesives, and specially manufactured attachment devices.
When the pump is being installed in the well, the pump cable is subjected to a risk of damage due to abrasion and crushing. The risks are significantly increased when the pump is run through a deviated section of the well. Frequently, a flat, steel-armored cable is used to mitigate these risks; however, this special cable is expensive and still only provides an incremental level of reduced risk.